1. Field of the Invention
The present invention relates to methods and devices that make it possible to authorize access to an instrument or apparatus on the basis of events that are independent of the user's will, by inhibiting the operation of the computer device used to the control the apparatus. It can be applied more particularly to the case of instruments that are rented out and for which checks are to be made, for example on the number of hours of use or on a rental limit date.
2. Description of the Prior Art
It is become increasingly frequent for all kinds of instruments, such as measuring instruments for example, to work under the control of a computerized operating system that generally comprises a microprocessor, an operating random-access memory, a saved memory comprising the programs of the system, keyboard type control devices and screen type display devices. These different devices are joined together by address, control and data buses in a structure that is very similar to that of PC type microcomputers. This multi-purpose type of structure can be applied to many instruments to collect data and send out commands by the simple adaptation, depending on the instrument used, of the control program contained in the memory of the computer system. Thus, costs are sharply reduced and it is furthermore possible to connect all these instruments together by means of standardized linking devices, whether at the level of the buses themselves, such as IEEE type buses or at the level of series or parallel type links.
Current practice, which is related to problems of costs and rapid obsolescence, is leading industrialists to take these instruments out on rent instead of purchasing them. The renting-out party naturally wishes to have guarantees regarding possible misuse of the instrument by limiting the rental period, for example, to a certain number of hours for instruments that wear out during operation, or to a certain duration to prevent the instrument from continuing to function if the customer should keep it or if the instrument should disappear.
To this end, it has been thought of using counter type or calendar clock type systems which, for example, cut off the power supply to the instrument. Until now, these different systems have not been very satisfactory because it is fairly easy to infringe their limits.